Lean Six Sigma Yellow Belt Certification Lean Six Sigma Yellow Belt Control and Sustainment Methods 1 — Questions and Answers
Question 1: What is the primary purpose of a Control Plan in the Control phase of DMAIC?
- To document the project timeline and team responsibilities
- To specify what process variables to monitor, how to measure them, the sampling frequency, and the response if limits are exceeded (Correct answer)
- To summarize the financial savings achieved by the project
- To replace the project charter once improvements are implemented
Correct answer: To specify what process variables to monitor, how to measure them, the sampling frequency, and the response if limits are exceeded
A Control Plan is a structured document that defines which key inputs and outputs to monitor, the measurement method and frequency, acceptable limits, and the required response action when a process goes out of control — ensuring improvements are maintained.
Question 2: Which type of control chart is most appropriate for tracking the number of defects found in a fixed-size sample?
- X-bar and R chart
- p-chart
- c-chart (Correct answer)
- I-MR chart
Correct answer: c-chart
The c-chart (count chart) is used when counting the number of defects (nonconformities) per unit when the sample size is constant. The p-chart tracks the proportion defective, while X-bar/R and I-MR charts are used for continuous measurement data.
Question 3: In Statistical Process Control, a process is said to exhibit 'common cause variation' when:
- Data points fall outside the control limits in a random pattern
- The process shows consistent, random variation within control limits with no non-random patterns (Correct answer)
- Seven consecutive points appear on the same side of the centerline
- The process average suddenly shifts after an equipment change
Correct answer: The process shows consistent, random variation within control limits with no non-random patterns
Common cause variation is the natural, inherent variability in a stable process — data points fluctuate randomly within the control limits. Special cause variation, by contrast, produces non-random patterns such as runs, trends, or points outside control limits.
Question 4: Mistake-proofing (poka-yoke) is most accurately described as:
- Training employees to double-check their own work before moving to the next step
- Adding a final inspection station at the end of the production line
- Redesigning the process or equipment so that errors are physically impossible or immediately detected and flagged (Correct answer)
- Updating the Standard Operating Procedure to include error-prevention reminders
Correct answer: Redesigning the process or equipment so that errors are physically impossible or immediately detected and flagged
Poka-yoke devices or design changes prevent errors at the source by making incorrect actions impossible (prevention) or by immediately signaling when an error occurs (detection). It is a stronger control mechanism than training or inspection alone.
Question 5: When a control chart signals an out-of-control condition, what should the process operator do first?
- Immediately stop the process and wait for management approval to restart
- Follow the pre-defined reaction plan documented in the Control Plan (Correct answer)
- Begin a new DMAIC project to investigate the root cause
- Adjust the control limits to accommodate the variation
Correct answer: Follow the pre-defined reaction plan documented in the Control Plan
A reaction (or response) plan is established during the Control phase precisely for this scenario. It tells operators the immediate containment steps to take when an out-of-control signal appears, ensuring a fast, consistent response without waiting for management or starting a lengthy analysis.
Question 6: Which sustainment tool provides a visual, at-a-glance view of key process metrics and their current performance status, allowing teams to quickly identify when results are drifting from targets?
- SIPOC diagram
- Performance dashboard or scorecard (Correct answer)
- Cause-and-effect matrix
- Value stream map
Correct answer: Performance dashboard or scorecard
A performance dashboard or scorecard consolidates the most important process metrics into a single visual display, often using color coding (e.g., green/yellow/red) to signal whether each metric is on target. This enables rapid detection of deterioration so corrective action can be taken before gains are lost.
Lean Six Sigma Yellow Belt Certification Lean Six Sigma Yellow Belt Control and Sustainment Methods 1
What is the primary purpose of a Control Plan in the Control phase of DMAIC?